Electrophoresis is a relatively old technique and is used to separate, identify, and purify DNA fragments. Electrophoresis techniques are capable of resolving mixtures of DNA fragments that cannot be separated adequately with other sizing procedures, such as density gradient centrifugation. Agarose gel electrophoresis was introduced many years ago, and since then, many different designs of apparatus have been used. Almost all agarose gel electrophoresis is performed on horizontal slab gels, which have several advantages over vertical gels. For example, a relatively low agarose concentration can be used because the entire gel is supported from beneath, gels can be cast in various sizes, and generally the apparatus is usually durable and inexpensive to construct. Gel electrophoresis is generally performed by casting a gel on a glass or plastic plate, or an ultraviolet-transparent (UV-transparent) acrylic gel bed. The plate or gel bed is then installed on a platform so that the gel is submerged just beneath the surface of the liquid electrophoresis buffer. Electrodes are positioned adjacent the edges of the rectangular shaped gel and a voltage difference applied to the electrodes permitting a current to flow through the buffer and gel. The resistance to the passage of electric current of the gel is almost the same as that of the buffer, so a considerable fraction of the applied current passes along the length of the gel. At low voltages, the rate of migration of linear DNA fragments is proportional to the voltage applied and time of application. As the electric field strength is raised, the mobility of high molecular weight fragments of DNA is increased differentially. Accordingly, the effective range of separation of agarose gels decreases as the voltage is increased. Therefore, to obtain maximum resolution of DNA fragments, gels are generally run at a relatively low voltage, which necessarily increases processing time. The location of DNA within the gel can be determined directly by staining. Bands of DNA in the gel are stained with low concentrations of the fluorescent, intercalating dye ethidium bromide. As little as one nanogram of DNA can be detected by direct examination of the gel in ultraviolet light. The electrophoretic migration rate of DNA in agarose gels is dependent upon four main parameters, the molecular size of the DNA, the agarose concentration, the conformation of the DNA, and the applied current.
In recent years, several patents have been granted to devices which purported to improve the gel electrophoresis process. One such prior electrophoresis apparatus and method is disclosed in U.S. Pat. No. 5,582,702 entitled "Apparatus And Method For Electrophoresis" issuing to Cabilly et al on Dec. 10, 1996, which is herein incorporated by reference. Therein disclosed is a substantially closed cassette with a gel contained therein with the ions, cations and anions, required to drive the electrophoretic separation provided by a cation exchange matrix and an anion exchange matrix. The gel, ion exchange matrixes and conductive rods are all in contact and are immersed in a liquid buffer solution. Another device is disclosed in U.S. Pat. No. 5,637,202 entitled "Porous Electrophoresis Sponges" issuing to Harrington et al on Jun. 10, 1997, which is herein incorporated by reference. Therein disclosed is a porous plastic electrophoresis sponge that is intended to replace the gel normally cast in conventional electrophoresis methods. The sponge and attached electrodes are immersed in electrophoresis buffer and used in the same manner as any conventional electrophoresis material. Another device and method is disclosed in U.S. Pat. No. 4,954,236 entitled "Apparatus And Method For Gel Casting And Electrophoresis In A Single Enclosure" issuing to Kushner et al on Sep. 4, 1990, which is herein incorporated by reference. Therein disclosed is an enclosure used to precast gel slabs permitting sealing or subsequent unsealing when the assembly is inserted into a slab type electrophoresis cell designed for gel enclosures with step profiles.
While many of these prior devices function adequately, all require the gels to be submerged in a liquid buffer. Accordingly, many of these devices are difficult to move without spilling buffer, prone to leak electrically-charged buffer, and require that gels be cast in a separate casting device and then relocated to a buffer chamber for performing the gel electrophoresis. Additionally, there is a need to increase efficiencies and simplify the method of performing gel electrophoresis, including decreasing the time required to perform various testing procedures. While these prior patents have advanced the art of electrophoresis, they still require emerging the gel in a buffer solution which has the disadvantages indicated above. Accordingly, there is a continuing need to improve the art of electrophoresis making it simpler and quicker, while reducing the risk of spills of potentially hazardous buffer solutions.